This type of ancillary tool, commonly called “gripper/impactor tool”, is used during surgical operations for implanting a rigid acetabulum, generally made of metal, in the patient's hip. Once the acetabulum has been implanted in the bone, a polymer cup is housed in the acetabulum, this cup being itself intended to receive the hemispherical head of a femoral implant or of the anatomical femur. The polymer cup is either connected directly to the acetabulum, by wedging of corresponding truncated surfaces borne by the cup and the acetabulum, or connected to a metallic shell which is received in articulated manner, substantially in the manner of a ball-and-socket joint, in the acetabulum fixed to the bone. A cotyloidal assembly with double mobility is spoken of in the latter case.
A first example of this type of ancillary tool consists in a rigid handle at the distal end of which is permanently connected a head made of supple plastics material, such as Ertafluor (Registered Trademark). This head, whose outer dimensions are slightly greater than the inner dimensions of the acetabulum to be implanted, is introduced and wedged in this acetabulum, allowing gripping then positioning thereof up to the location of impaction of the hip. However, the use of such a one-piece head presents numerous drawbacks, as the supple material used does not allow an efficient grip if the inner dimensions of the acetabulum are not adapted to those of the head, this often obliging the surgeon to seize the acetabulum to be implanted in one hand, in order to wedge the head efficiently. The conditions of sterility are therefore not always respected. Moreover, the supple material of the head is often difficult to sterilize. Furthermore, once the impaction of the acetabulum is effected, it is generally difficult to disengage the head wedged in the acetabulum.
U.S. Pat. No. 5,169,399 discloses another example of such a tool in which a gripper/impactor handle is adapted for positioning a prosthetic assembly constituted by a metallic acetabulum and a polymeric insert, the acetabulum and the insert being positioned and impacted simultaneously by the handle. The latter presents at its distal end a split head whose two jaws are spaced apart from each other by a compression spring. When the surgeon brings the two jaws towards each other by compressing the spring, the head may be introduced inside the polymeric insert, then, by releasing one of the jaws, the prosthetic assembly formed by the insert and the acetabulum retained on the insert undergoes a gripping effort by the head. This tool is complex to make and to manipulate, the effort of grip depending directly on the force of the compression spring interposed between the jaws of the head. Moreover, insofar as the zone of contact between the head of the tool and the prosthetic assembly is formed by the end part of the polymeric insert of greatest diameter, the effort of impaction applied by the handle on the prosthetic assembly cannot attain high values without risk of damage to the insert and the guiding of the acetabulum by the head during impaction is unreliable. Under these conditions, there is no guarantee that the surgeon will not use one of his hands to hold the prosthetic assembly during grip thereof by the tool. Furthermore, this tool is not applicable to the positioning of a cotyloidal assembly with double mobility set forth hereinabove, the grip of the insert not ensuring hold of the acetabulum to be implanted.
Document WO 95/11641 discloses another tool of the afore-mentioned type, which further comprises a metallic endpiece removably added to the distal end of the handle for manipulating the acetabulum to be implanted. A deformable member of the endpiece is constituted by four quadrants, namely two diametrically opposite rigid quadrants fixedly connected to a proximal part of the endpiece by bridges of matter, and two diametrically opposite mobile quadrants, each connected to one of the rigid quadrants by an elastically deformable hinge. Pivoting of the two mobile quadrants is controlled by screwing the handle in the proximal part of the endpiece. However, the use of these two mobile quadrants ensures an efficient wedging of the acetabulum only in two diametrically opposite zones of its inner face, in other words only with a limited gripping force.
It is an object of the present invention to propose a tool which is adapted to acetabula of different dimensions and nature and which ensures both an efficient grip of the acetabulum and a good application of the force of impaction, without hindering the withdrawal of the tool once positioning has been effected.